Methods and system for determining compressor recirculation valve sludge

ABSTRACT

Systems and methods for determining the presence or absence of deposits that may accumulate within a compressor recirculation valve positioned in parallel with a turbocharger compressor are presented. The systems and methods adjust actuators to maintain engine operation such that it may be more difficult for a driver to become aware that a compressor recirculation valve diagnostic is being executed.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/566,442, entitled “METHODS AND SYSTEM FOR DETERMININGCOMPRESSOR RECIRCULATION VALVE SLUDGE,” filed on Dec. 10, 2014, now U.S.Pat. No. 9,631,564, the entire contents of which are incorporated hereinby reference for all purposes.

FIELD

The present description relates to methods and a system for determiningwhether or not sludge may have accumulated within a compressorrecirculation valve. The methods and systems may be particularly usefulin engines having turbochargers or superchargers.

BACKGROUND AND SUMMARY

A supercharged or turbocharged engine may include a compressorrecirculation valve for relieving pressure downstream of a compressorduring conditions where it may not be desirable to provide greaterpressure than atmospheric pressure upstream of a throttle. For example,if a driver is requesting a relatively high driver demand torquefollowed by a low driver demand torque, it may be desirable to reducepressure upstream of an engine intake manifold throttle so that theengine may provide torque closer to the driver demand torque. Thepressure downstream of a compressor may be relieved via opening acompressor recirculation valve in response to the low driver demandtorque. However, air in an engine intake system may be mixed with fuelvapors and contaminants that may pass through the engine's air intakefilter. The fuel vapors and contaminants may build up over time in thecompressor recirculation valve causing a change in the compressorrecirculation valve's flow characteristics. Therefore, the compressorrecirculation valve may not provide an expected amount of airflow duringsome conditions.

The inventors herein have recognized the above-mentioned issues and havedeveloped a diagnostic method, comprising: partially opening a wastegate and adjusting a compressor recirculation valve to a closed positionin response to a diagnostic request; incrementally opening thecompressor recirculation valve after the compressor recirculation valveis closed; adjusting a compressor recirculation valve airflow offset inresponse to waste gate position while incrementally opening thecompressor recirculation valve from the closed position; and operatingthe compressor recirculation valve in response to the airflow offset.

By adjusting a compressor recirculation valve airflow offset in responseto a waste gate position, it may be possible to provide the technicalresult of improving engine air intake pressure control even whendeposits are formed within a compressor recirculation valve. In oneexample, the recirculation valve airflow offset may be determined basedon a change in position of the waste gate when the waste gate is closedloop controlled to maintain a desired pressure at an inlet of an engineintake manifold throttle. Specifically, the recirculation valve may befirst closed and then incrementally opened. The recirculation valveopening position where the waste gate position is changed to maintainconstant engine intake manifold throttle inlet pressure may bedetermined to be the compressor recirculation valve offset value. Thewaste gate position may be adjusted in response to pressure at the inletof the engine intake manifold throttle to maintain engine airflow andreduce the possibility of disturbing a driver.

The present description may provide several advantages. For example, theapproach may improve engine airflow at low driver demand levels.Further, the approach may improve engine air-fuel ratio control duringaccelerator pedal tip-out conditions. Further, the approach may beapplied to turbocharged or supercharged engines.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is a plot shown flow of a throttle and flow of a throttle withdeposits;

FIG. 3 shows an example method for operating an engine; and

FIG. 4 shows an engine operating sequence based on the method of FIG. 3.

DETAILED DESCRIPTION

The present description is related to operating an engine with acompressor recirculation valve. The compressor recirculation valve maybe incorporated into an engine as is shown in FIG. 1. The compressorrecirculation valve may exhibit flow characteristics similar to thoseshown in FIG. 2. The engine may be part of a system that includes acontroller with instructions for the method of FIG. 3. The system ofFIG. 1 and the method of FIG. 3 may operate to provide the sequence ofFIG. 4.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Flywheel 97 and ring gear 99 arecoupled to crankshaft 40. Starter 96 (e.g., low voltage (operated withless than 30 volts) electric machine) includes pinion shaft 98 andpinion gear 95. Pinion shaft 98 may selectively advance pinion gear 95to engage ring gear 99. Starter 96 may be directly mounted to the frontof the engine or the rear of the engine. In some examples, starter 96may selectively supply torque to crankshaft 40 via a belt or chain. Inone example, starter 96 is in a base state when not engaged to theengine crankshaft. Combustion chamber 30 is shown communicating withintake manifold 44 and exhaust manifold 48 via respective intake valve52 and exhaust valve 54. Each intake and exhaust valve may be operatedby an intake cam 51 and an exhaust cam 53. The position of intake cam 51may be determined by intake cam sensor 55. The position of exhaust cam53 may be determined by exhaust cam sensor 57. Intake valve 52 may beselectively activated and deactivated by valve activation device 59.Exhaust valve 54 may be selectively activated and deactivated by valveactivation device 58.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Fuel injector 66 delivers liquid fuel in proportion to thepulse width from controller 12. Fuel is delivered to fuel injector 66 bya fuel system (not shown) including a fuel tank, fuel pump, and fuelrail (not shown). In one example, a high pressure, dual stage, fuelsystem may be used to generate higher fuel pressures.

In addition, intake manifold 44 is shown communicating with turbochargercompressor 162 and engine air intake 42. In other examples, compressor162 may be a supercharger compressor. Shaft 161 mechanically couplesturbocharger turbine 164 to turbocharger compressor 162. Optionalelectronic throttle 62 (e.g., central or engine intake manifoldthrottle) adjusts a position of throttle plate 64 to control air flowfrom compressor 162 to intake manifold 44. Pressure in boost chamber 45may be referred to as throttle inlet pressure since the inlet ofthrottle 62 is within boost chamber 45. The throttle outlet is in intakemanifold 44. In some examples, throttle 62 and throttle plate 64 may bepositioned between intake valve 52 and intake manifold 44 such thatthrottle 62 is a port throttle. Compressor recirculation valve 47 may beselectively adjusted to a plurality of positions between fully open andfully closed. Waste gate 163 may be adjusted via controller 12 to allowexhaust gases to selectively bypass turbine 164 to control the speed ofcompressor 162.

Air filter 43 cleans air entering engine air intake 42 via inlet 3 whichis exposed to ambient temperature and pressure. Combustion byproductsare exhausted at outlet 5 which is exposed to ambient temperature andpressure. Piston 36 and combustion chamber 30 operate as a pump whenengine 10 rotates and combusts air and fuel. Air is drawn from inlet 3and exhaust products are expelled at outlet 5. Inlet 3 is upstream ofoutlet 5 according to the direction of flow through engine 10, exhaustmanifold 48, and engine air intake 42. Upstream of engine 10 does notinclude anything outside the engine past the inlet, and downstream ofengine 10 does not include anything outside the engine past the outlet.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106 (e.g., non-transitory memory), random access memory 108, keepalive memory 110, and a conventional data bus. Controller 12 is shownreceiving various signals from sensors coupled to engine 10, in additionto those signals previously discussed, including: engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a position sensor 134 coupled to an accelerator pedal 130 forsensing force applied by foot 132; a position sensor 154 coupled tobrake pedal 150 for sensing force applied by foot 152, a measurement ofengine manifold pressure (MAP) from pressure sensor 123 coupled tointake manifold 44; a measurement of engine boost pressure or throttleinlet pressure from pressure sensor 122; an engine position from a Halleffect sensor 118 sensing crankshaft 40 position; a measurement of airmass entering the engine from sensor 120; and a measurement of throttleposition from sensor 68. Barometric pressure may also be sensed (sensornot shown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC).

During the compression stroke, intake valve 52 and exhaust valve 54 areclosed. Piston 36 moves toward the cylinder head so as to compress theair within combustion chamber 30. The point at which piston 36 is at theend of its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion.

During the expansion stroke, the expanding gases push piston 36 back toBDC. Crankshaft 40 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve54 opens to release the combusted air-fuel mixture to exhaust manifold48 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

The system of FIG. 1 provides for a system, comprising: an engine; aturbocharger including a compressor mechanically coupled to the engine,the turbocharger including a waste gate; a recirculation valvepositioned in an air intake of the engine in parallel with thecompressor; and a controller including instructions stored innon-transitory memory for adjusting a position of the waste gate tomaintain engine intake manifold throttle inlet pressure at a constantpressure and adjust a transfer function of the recirculation valve inresponse to a position of the recirculation valve that causes theposition of the waste gate to be adjusted to maintain engine intakemanifold throttle inlet pressure. The system further comprisesadditional instructions to closed loop control the waste gate tomaintain engine intake manifold throttle inlet pressure.

In some examples, the system includes where an offset value of thetransfer function is adjusted. The system further comprises additionalinstructions to incrementally open the recirculation valve. The systemincludes where the position of the recirculation valve is a positionwhere air begins to recirculate from an output of a compressor to aninlet of the compressor. The system further comprises additionalinstructions for exiting a recirculation valve diagnostic mode inresponse to an increase in driver demand torque. The system furthercomprises additional instructions to operate the recirculation valve inresponse to the transfer function.

Referring now to FIG. 2, a prophetic plot of airflow versus compressorrecirculation valve angle for a fixed pressure drop across a compressorrecirculation valve is shown. The X axis represents compressorrecirculation valve angle. The angle increases in the direction of the Xaxis arrow and the compressor recirculation valve opening amountincreases as the angle increases. The Y axis represents airflow throughthe compressor recirculation valve. Curve 202 represents characteristicsfor a compressor recirculation valve that is free of deposits, and curve204 represents characteristics for a compressor recirculation valve thathas deposits. Deposits may form from fuel vapors and/or materialinducted into the engine. Curves 202 and 204 may be referred to ascompressor recirculation valve transfer functions since they describecompressor recirculation input (e.g., angle) versus output (e.g.,airflow) for a given pressure ratio across the compressor recirculationvalve.

The plot shows that the compressor recirculation valve with deposits(e.g., curve 204) begins to allow air flow at a greater angle than thecompressor recirculation valve without deposits (e.g., curve 202). Thedeposits may partially restrict flow through the compressorrecirculation valve. Therefore, if a controller adjusts an angle of thecompressor recirculation valve with deposits, there may not be airflowfor conditions where the controller is expecting airflow. Consequently,it may be more difficult to control pressure at a location upstream of acentral throttle or engine intake manifold throttle. Leader 210 shows anoffset between curve 202 and curve 204. The offset represents acompressor recirculation valve angle difference between where airflowbegins through the compressor recirculation valve without deposits andthe compressor recirculation valve with deposits. Thus, by determiningwhen airflow begins through the compressor recirculation valve, theoffset in compressor recirculation valve angle may be determined.

Referring now to FIG. 3, a method for operating an engine is shown. Themethod of FIG. 3 may provide the operating sequence shown in FIG. 4.Additionally, the method of FIG. 3 may be included in the system of FIG.1 as executable instructions stored in non-transitory memory.

At 302, method 300 judges if conditions are present for adapting acompressor recirculation valve transfer function. In one example,conditions may be present for adapting or revising a compressorrecirculation valve transfer function when the engine is operatingwithin a predetermined engine speed and load range. A request to enter acompressor recirculation valve diagnostic mode may be made in responseto conditions being present for adapting the compressor recirculationvalve transfer function. Further, it may be desirable to operate theengine at a substantially constant engine speed and load (e.g., changingby less than five percent). If method 300 judges that conditions arepresent for adapting the compressor recirculation valve transferfunction, the answer is yes and method 300 proceeds to 304. Otherwise,the answer is no and method 300 proceeds to 314.

At 314, method 300 operates the compressor recirculation valve based onthe compressor recirculation valve's present transfer function. Forexample, if the pressure in the boost chamber or inlet of the engine'sthrottle is greater than desired, the compressor recirculation valve maybe adjusted to an angle where airflow through the compressorrecirculation valve begins to increase based on the compressorrecirculation valve's transfer function. In this way, the engine intakemanifold throttle inlet pressure may be maintained at a desired level.In some examples, the compressor recirculation valve position may beadjusted in response to a difference between a desired engine throttleinlet pressure and an actual engine throttle inlet pressure. Method 300proceeds to exit after the compressor recirculation valve position isadjusted according to the present compressor recirculation valvetransfer function.

At 304, method 300 fully closes the compressor recirculation valve. Byclosing the compressor recirculation valve, it may be established thatairflow through the compressor recirculation valve is substantially zero(e.g., less than one percent of maximum flow through the compressorrecirculation valve). Method 300 proceeds to 306 after the compressorrecirculation valve is closed.

At 306, method 300 positions the turbocharger waste gate to maintain apredetermined desired engine intake manifold throttle inlet pressure. Inone example, the turbocharger waste gate is closed loop controlled toprovide a desired pressure at an inlet of an engine intake manifoldthrottle. If pressure at the inlet is too low, the waste gate is atleast partially closed. If pressure at the inlet is too high, the wastegate is at least partially opened. Engine intake manifold pressure maybe subtracted from a desired engine intake manifold pressure to providean error value, and the error value may be multiplied by proportionaland integral terms. The result of multiplying the error by theproportional term may be added to the result of multiplying the error bythe integral term. The result of the addition may be the basis foradjusting the waste gate position. Method 300 proceeds to 308 after thewaste gate position is adjusted.

At 308, method 300 increments the compressor recirculation valve openingamount by a predetermined amount (e.g., two degrees). The predeterminedamount may be based on the present engine speed and load. Byincrementing the compressor recirculation valve opening amount, thecompressor recirculation valve opening amount is increased. Air flowsfrom the compressor outlet to the compressor inlet when the compressorrecirculation valve is opened sufficiently to allow airflow. Method 300proceeds to 310 after the compressor recirculation valve opening amounthas been incremented.

At 310, method 300 judges if there has been a change in driver demandtorque greater than an absolute threshold amount after the compressorrecirculation valve was closed at 304. If so, the answer is yes andmethod 300 proceeds to 314 and exits the compressor recirculation valveadaption or revision mode. Otherwise, the answer is no and method 300proceeds to 312.

At 314, method 300 stores the present compressor recirculation valve(CRV) position, waste gate position, and central throttle inlet pressureto controller memory. The compressor recirculation valve position, thecentral throttle position, and the central throttle inlet pressure maybe measured or inferred. Method 300 proceeds to 316 after the presentcompressor recirculation valve position, waste gate position, andcentral throttle inlet pressure are stored to controller memory.

At 316, method 300 judges if the compressor recirculation valve is openmore than a predetermined amount. In one example, the predeterminedamount is a value greater than twenty five percent of the compressorrecirculation valve's total opening amount. If the compressorrecirculation valve opening amount has been incremented to a valuegreater than the threshold amount, the answer is yes and method 300proceeds to 316. Otherwise, the answer is no and method 300 returns to306.

At 316, method 300 updates or revises the offset value in the compressorrecirculation transfer function. In one example, the offset is acompressor recirculation valve angle where flow through the compressorrecirculation valve is determined based on a change in turbochargerwaste gate position. For example, if the compressor recirculation valveopens and the waste gate is closed to maintain pressure at the inlet ofthe central throttle, the valve angle of the offset is the compressorrecirculation valve angle where the waste gate position changed (e.g.,closed). In particular, the offset may be established where the wastegate closes in response to the central throttle opening amountincreasing after the compressor recirculation is closed and constantengine manifold throttle inlet pressure is established. The waste gateopening decreasing based on closed loop waste gate control to maintainconstant engine intake manifold inlet pressure. Additionally, theremaining values in the compressor recirculation valve's transferfunction may be adjusted based on the new offset value. In one example,predetermined amounts (e.g., compressor recirculation valve angleincreases) are added to the present values in the compressorrecirculation valve transfer function based on the new offset value. Forexample, if the new offset value is increased from two degrees to fourdegrees, the compressor recirculation valve angle that corresponds to aflow rate of X Kg/sec may be increased by two degrees. The two degreeincrease may be empirically determined and stored to memory based on thepresent compressor recirculation valve offset. Additionally, all otherentries in the compressor recirculation valve transfer function may berevised in a similar way. Method 300 proceeds to 324 after thecompressor recirculation valve transfer function is revised.

At 320, method 300 operates the compressor recirculation valve based onthe revised compressor recirculation valve transfer function accordingto predetermined scheduled operation. For example, if pressure at thethrottle inlet is greater than desired, the compressor recirculationvalve position may be adjusted to the offset value so that air flowsthrough the compressor recirculation valve, thereby reducing thethrottle inlet pressure. Additionally, the engine throttle and wastegate are operated according to schedule (e.g., based on engine speed,load, and driver demand torque). Thus, engine throttle control, wastegate control, and compressor recirculation valve control are returned tostandard operation when the compressor recirculation valve adaption modeis complete. Method 300 proceeds to exit after the waste gate andcompressor recirculation valve resume standard operation.

Thus, the method of FIG. 3 provide for a diagnostic method, comprising:partially opening a waste gate and adjusting a compressor recirculationvalve to a closed position in response to a diagnostic request;incrementally opening the compressor recirculation valve after thecompressor recirculation valve is closed; adjusting a compressorrecirculation valve airflow offset in response to waste gate positionwhile incrementally opening the compressor recirculation valve from theclosed position; and operating the compressor recirculation valve inresponse to the airflow offset. The method includes where the diagnosticrequest is a request to adjust the compressor recirculation valveairflow offset. The method further comprises adjusting the waste gateposition in response to an throttle inlet pressure.

In some examples, the method includes where the waste gate position isadjusted to maintain a pressure at a throttle inlet. The method includeswhere the waste gate position is closed while incrementally opening thecompressor recirculation valve. The method includes where therecirculation valve is incrementally opened during a recirculation valveadaptation mode, and further comprising exiting the recirculation valveadaptation mode in response to an increase in driver demand torque. Themethod includes where the recirculation valve airflow offset is anopening position of the recirculation valve where airflow greater than athreshold amount is present.

The method of FIG. 3 also provides for a diagnostic method, comprising:partially opening a waste gate, adjusting a compressor recirculationvalve to a closed position, and maintaining a constant engine throttleinlet pressure via adjusting a position of the waste gate in response toa diagnostic request; incrementally opening the compressor recirculationvalve after the compressor recirculation valve is closed; adjusting arecirculation valve transfer function in response to a position of thecompressor recirculation valve where the waste gate position is firstadjusted after the compressor recirculation valve is closed and theconstant engine throttle inlet pressure is maintained; and operating therecirculation valve in response to the recirculation valve transferfunction. The method includes where waste gate is closed in response toa reduction in engine throttle inlet pressure. The method includes wherethe diagnostic request is a compressor recirculation valve diagnosticrequest.

In some examples, the method includes where the diagnostic requestinitiates a diagnostic mode, and further comprising holding an engineintake manifold throttle at a constant position during the diagnosticmode. The method further comprises exiting the diagnostic mode inresponse to an increase in driver demand torque. The method alsoincludes where the compressor recirculation valve is positioned inparallel with a compressor.

Referring now to FIG. 4, a sequence for operating an engine according tothe method of FIG. 3 is shown. The sequence may be provided via thesystem of FIG. 1. Vertical lines at time T1-T3 represent times ofinterest during the sequence.

The first plot from the top of FIG. 4 is a plot of compressorrecirculation valve (CRV) position versus time. The Y axis representsCRV position and the CRV opening amount increases in the direction ofthe Y axis arrow. The X axis represents time and time increases from theleft side of the figure to the right side of the figure.

The second plot from the top of FIG. 4 is a plot of turbocharger wastegate position versus time. The Y axis represents turbocharger waste gateposition and the waste gate opening amount increases in the direction ofthe Y axis arrow. The X axis represents time and time increases from theleft side of the figure to the right side of the figure.

The third plot from the top of FIG. 4 is a plot of the engine's centralthrottle position versus time. The Y axis represents central throttleposition and the central throttle opening amount increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left side of the figure to the right side of thefigure.

The fourth plot from the top of FIG. 4 is a plot of driver demand torqueversus time. The Y axis represents driver demand torque and driverdemand torque increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left side of the figure tothe right side of the figure.

The fifth plot from the top of FIG. 4 is a plot of engine centralthrottle inlet pressure versus time. The Y axis represents enginecentral throttle inlet pressure versus time and the engine throttleinlet pressure increases in the direction of the Y axis arrow. The Xaxis represents time and time increases from the left side of the figureto the right side of the figure.

At time T0, the engine is not in a compressor recirculation valvediagnostic mode and the CRV position is partially open and the wastegate is partially open. The central throttle is partially open and thedriver demand torque is a middle level. The engine throttle inletpressure is at a middle level. These conditions may be indicative ofoperating the engine at part load.

At time T1, the engine enters a CRV diagnostic mode in response tooperating conditions being conducive to updating a CRV transferfunction. The CRV closes in response to entering the CRV diagnosticmode. The waste gate remains open and the central throttle is alsopartially open. The waste gate is closed loop controlled to maintain aconstant engine intake manifold inlet pressure at a predeterminedconstant value. In one example, the waste gate position may be adjustedin response to central throttle inlet pressure. The driver demand torqueand the central throttle inlet pressure remain at middle levels.

Between time T1 and time T2, the diagnostic is active and the CRVposition is incremented in an effort to determine an angle where airbegins to flow through the CRV. The waste gate remains partially open,the central throttle position remains unchanged, and the driver demandtorque remains unchanged.

At time T2, compressor bypass valve position reaches an amount where airstarts to flow through the compressor bypass valve. The airflow throughthe compressor bypass valve lowers pressure at the central throttleinlet, and the waste gate opening amount is decreased so that acompressor output may be increased to maintain a constant centralthrottle inlet pressure. The angle of the compressor bypass valve attime T2 is indicated by leader 405, the angle may be determined to be anoffset value for a transfer function for the compressor bypass valve.The angle at 405 may be established as a compressor bypass valve anglewhere the waste gate position was adjusted after the compressorrecirculation valve was closed and a constant engine intake manifoldthrottle inlet pressure was provided for the engine. The driver demandtorque and the central throttle position remain unchanged.

At time T3, the compressor recirculation valve reaches a threshold valuewhere the compressor recirculation valve diagnostic is ceased. Forexample, the compressor recirculation valve diagnostic may be ceasedwhen the compressor recirculation valve opens more than twenty fivepercent of full scale opening amount. The compressor recirculation valveis closed or returned to a value based on present engine operatingconditions. Further, the waste gate position is adjusted in response toclosing the compressor recirculation valve. Consequently, the centralthrottle inlet pressure is maintained in response to closing thecompressor recirculation valve.

In this way, the compressor recirculation valve offset may be determinedbased on a waste gate and/or a central throttle inlet pressure. Further,the remaining values in the compressor recirculation valve transferfunction may be adjusted in response to the revised offset value.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

The invention claimed is:
 1. A diagnostic method, comprising: partiallyopening a waste gate and adjusting a compressor recirculation valve to aclosed position in response to a diagnostic request; incrementallyopening the compressor recirculation valve after the compressorrecirculation valve is closed while maintaining engine intake manifoldthrottle inlet pressure and while determining an angle where air beginsto flow through the compressor recirculation valve; and operating thecompressor recirculation valve in response to the determined angle. 2.The method of claim 1, where the throttle is positioned downstream of aturbocharger compressor in an engine intake system.
 3. The method ofclaim 1, further comprising adjusting a waste gate position in responseto the engine intake manifold throttle inlet pressure.
 4. The method ofclaim 3, wherein a position of a throttle remains unchanged whilemaintaining the engine intake manifold throttle inlet pressure.
 5. Themethod of claim 4, where the waste gate position is closed whileincrementally opening the compressor recirculation valve.
 6. The methodof claim 1, where the compressor recirculation valve is incrementallyopened during a compressor recirculation valve adaptation mode, andfurther comprising exiting the compressor recirculation valve adaptationmode in response to an increase in driver demand torque.
 7. The methodof claim 6, where the driver demand torque remains unchanged whileincrementally opening the compressor recirculation valve.
 8. Adiagnostic method, comprising: partially opening a waste gate, adjustinga compressor recirculation valve to a closed position, and maintaining aconstant engine throttle inlet pressure via adjusting a position of thewaste gate in response to a diagnostic request; incrementally openingthe compressor recirculation valve after the compressor recirculationvalve is closed; determining an angle where air begins to flow throughthe compressor recirculation valve; adjusting a recirculation valvetransfer function in response to the determined angle; and operating thecompressor recirculation valve in response to the recirculation valvetransfer function.
 9. The method of claim 8, where the waste gate isclosed in response to a reduction in engine throttle inlet pressure. 10.The method of claim 8, where the diagnostic request is a compressorrecirculation valve diagnostic request.
 11. The method of claim 8, wherethe diagnostic request initiates a diagnostic mode, and furthercomprising holding an engine intake manifold throttle at a constantposition during the diagnostic mode.
 12. The method of claim 11, furthercomprising exiting the diagnostic mode in response to an increase indriver demand torque.
 13. The method of claim 8, where the compressorrecirculation valve is positioned in parallel with a compressor.
 14. Asystem, comprising: an engine; a turbocharger including a compressormechanically coupled to the engine, the turbocharger including a wastegate; a recirculation valve positioned in an air intake of the engine inparallel with the compressor; a throttle positioned downstream of thecompressor; and a controller including instructions stored innon-transitory memory for adjusting a position of the waste gate tomaintain engine intake manifold throttle inlet pressure at a constantpressure and determining an angle where air begins to flow through therecirculation valve in response to a position of the recirculation valvethat causes the position of the waste gate to be adjusted to maintainthe engine intake manifold throttle inlet pressure.
 15. The system ofclaim 14, further comprising additional instructions to closed loopcontrol the waste gate to maintain the engine intake manifold throttleinlet pressure.
 16. The system of claim 14, further comprisingadditional instructions to incrementally open the recirculation valve.17. The system of claim 14, further comprising additional instructionsfor exiting a recirculation valve diagnostic mode in response to anincrease in driver demand torque.
 18. The system of claim 14, furthercomprising additional instructions to operate the recirculation valve inresponse to a transfer function.